1. Field of the Invention
The present invention relates to a rotary electric machine, and an electric vehicle including the same.
2. Description of the Related Art
Drive motors used for electric vehicles or hybrid vehicles are required to output large power. Thus, permanent magnet type motors using a sintered magnet made of rare earth material for holding large energy is generally used. An embedded magnet type motor among the permanent magnet type motors is used as the drive motor which can satisfy requirements, including low-speed and large-torque output, and a wide range of rotation speeds.
Torque pulsation of the motor causes noise or vibration. In particular, the torque pulsation on the low-speed side of the electric vehicle disadvantageously deteriorates ride quality. In a conventional motor, a permanent magnet is generally skewed so as to reduce cogging torque. Instead of skewing the permanent magnet, JP-A-2005-176424 has proposed that a rotary electric machine is provided with slots on the outer peripheral side of the embedded magnet or the outer peripheral surface of a pole piece so as to reduce the cogging torque such that the slot is formed to be shifted in the direction of rotation as viewed from the direction of a rotation axis.
The occurrence of torque pulsation in a rotary electric machine is caused by the cogging torque due to a magnetic circuit for allowing a magnetic flux generated from a permanent magnet provided in a rotor to pass through a stator and then to return to the rotor again, and by a rotating magnetic flux generated by a current of the stator. The above-mentioned JP-A-176424/2005 relates to a technique for reducing the cogging torque as mentioned above.
The invention is directed to reduction of the pulsation due to the rotating magnetic flux generated by the stator current as mentioned above.
When the method disclosed in the above-mentioned JP-A-176424/2005 is intended to be used for reducing torque pulsation due to the stator current, which is to be solved by the invention, the appropriate reduction of the cogging torque becomes very difficult. That is, the method disclosed in JP-A-176424/2005 is designed to reduce the cogging torque. When the concept of this method is intended to be further applied so as to reduce the torque pulsation due to the stator current, the inherent cogging torque cannot be appropriately reduced.
General techniques proposed for reducing torque pulsation have the same influence on both of the cogging torque and the torque pulsation due to the stator current. As a result, in order to reduce both torque pulsations, it is necessary to handle the rotary electric machine taking into consideration the influence on both. This makes it difficult to easily solve both pulsations.
The inventors have thought that the entire torque pulsation can be more easily reduced and adjusted if the torque pulsation due to the stator current can be reduced by a structure or way which has little influence on the cogging torque. For example, when the cogging torque can be reduced and additionally the torque pulsation due to the stator current can also be reduced, the entire torque pulsation can be easily reduced.